The present invention relates to face masks in general, and particularly to an improved multi-layer face mask.
Multi-layer face masks are well known in the art. These face masks typically have a pleated configuration and contain at least one intermediate filtering layer disposed between an outside cover layer and an inner face cover layer. The cover layers, particularly the inner face layer, are generally formed of relatively lightweight and highly porous non-woven fabrics. The cover layers serve to retain the intermediate filtration layer or layers and also to provide a comfortable surface against the user""s face. A suitable face cover layer material may be a carded non-woven fabric bonded with a thermoplastic binder or adhesive.
Due to the relatively light weight of the individual layers of the mask, particularly the cover layers, the layers are typically bonded together so that they may be pleated and a seam binding applied in an automated production line. Additionally, the face cover layer is typically separately bonded to the filtration layer at certain points to prevent it from moving over the nose or mouth of the wearer as the wearer inhales. If the face cover layer is not bonded, it tends to move against the nose or mouth of the wearer and, although this does not reduce the efficiency of the mask, causes discomfort to the wearer.
The bonding of the face cover layer to the filtration layer has been carried out in various ways. For example, the bonding may be done by heat sealing the layers together with sufficient force to effectuate the bond through all layers of the mask. The filtration medium filaments are typically thermoplastic, and the application of heat and pressure causes the filaments to melt and, upon cooling, harden and form a permanent bond between the three layers of the mask. It is also known to employ hot melt adhesives, or other types of adhesive materials, to effectuate a spot bonding of the layers of the mask together. U.S. Pat. No. 3,802,429 teaches that six to nine bonded areas located between the folds of the mask are sufficient to bond the three layers of the mask into a unitary laminate. Each bonded area is approximately xe2x85x9 inch square and tends to be impervious to the passage of air through the mask.
Commercial examples of pleated masks having xe2x80x9cspotxe2x80x9d bonded areas are known in the art. The 1818 mask from 3M Corporation has an adhesive applied in a regular repeating xe2x80x9ctracksxe2x80x9d pattern over the entire surface of the three layer mask. The pattern can be seen on the outer cover layer of the mask since the adhesive is pigmented and causes a discoloration of the materials. Another commercial mask is the SoftTouch II mask formerly from Tecnol Medical Products. In this mask, the inner face layer is adhered to the filtration layer in a process wherein an adhesive is lightly sprayed over a center surface area strip between the filtration layer and the inner face layer.
A drawback with the present mask constructions is that adhesive bleed-through can be detrimental to the manufacturing process as a result of build-up on the equipment. Adhesive build-up on the production line surfaces makes collating and pleating of the layers extremely difficult and may cause shutdown of the equipment and production line. This problem is particularly acute when the adhesive is applied in a pattern or spray over the entire surface of the mask. An even more significant drawback is that the adhesive application is generally insufficient to keep the inner face layer attached to the filtration layer in all uses of the masks.
The present invention provides an improved mask while addressing the shortcomings of the conventional masks and production methods noted above.
Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In accordance with the invention, an improved multi-layer face mask is provided. The face mask includes a filter body having at least an outer cover layer, an inner face cover layer, and at least one intermediate layer, such as a filter layer, sandwiched between the face cover layer and outer cover layer. The filter body has at least one pleat formed therein that extends across the filter body. For example, the filter body may be defined by top and bottom edges, and side edges that extend between the top and bottom edges. The pleat extends longitudinally across the filter body between the side edges and is defined by generally parallel fold lines formed in the filter body layers. It should, however, be appreciated that the construction of the filter body and configuration of the pleats or fold lines is not particularly important to the present invention. Various styles of pleated face masks are known in the art and any such style is applicable to the present invention. For example, the pleats may be formed so as to open or unfold in one direction. In an alternative embodiment, oppositely facing pleats may be disposed on opposite sides of a center pleated panel. This configuration is well known from the 3M 1818 mask and the Tecnol Medical Products SoftTouch II mask.
It should also be appreciated that the particular types of materials used to form the layers of the face mask are not critical to the invention. Various types and combinations of materials are well known to those skilled in the art and any suitable materials or laminates may be used in a face mask in accordance with the present invention.
An adhesive is applied between the intermediate layer and the face layer in the manufacturing process of the mask prior to forming the pleat or pleats in the mask. The adhesive is applied along a plurality of longitudinal strips or sections across the filter body. For example, the strips may extend from one side edge of the mask to the other side edge of the mask. The adhesive strips are defined by longitudinal edges and may be applied in various ways. For example, the adhesive may be applied in a continuous application process wherein the adhesive is continuous or xe2x80x9cunbrokenxe2x80x9d along the longitudinal section or strip. For example, the adhesive may be coated or sprayed continuously along the strip. Coverage of the adhesive between the edges of the longitudinal strip may be total or less than total. For example, a swirl coating process would apply the adhesive continuously along the strip, but surface area coverage of the adhesive between the edges of the strip would be less than total. In an alternative embodiment, the adhesive may be applied in a discontinuous process, such a pattern spray or discontinuous coating process, such that the adhesive is applied in discrete sub-sections or patterns along the strip.
So as to further minimize the potential for adhesive bleed through in the manufacturing process, it may be desired to dispose the adhesive strip along a pleat formed in the face mask. In this embodiment, the adhesive strip may have a width so as to extend at least between the fold lines of the pleat. Alternatively, the adhesive strip may extend beyond each of the fold lines a distance about equal to the overlap width of the subsequently formed pleat. It may be desired to provide such an adhesive strip for each pleat formed in the face mask.
A method for manufacturing an improved multi-layer face mask is also provided. The method includes applying an adhesive between the intermediate layer and the face cover layer of the mask along longitudinal strips or sections across the layers. This longitudinal strips are disposed between defined longitudinal lines or edges in varying degrees of coverage or patterns. For example, the adhesive may be sprayed along the strip in a continuous process for relatively complete or total coverage. In an alternative embodiment, the adhesive may be sprayed or coated in a pattern between the longitudinal edges.
Once the longitudinal adhesive strips are applied and the face layer and intermediate layer are bonded, a pleat is formed in the layers along at least one of the adhesive strips. The pleat is formed by parallel fold lines and the adhesive strip may be applied with a width so as to extend at least between the fold lines. The strip may extend beyond the fold lines a distance generally equal to the overlap width of the pleat.
By applying the adhesive in a generally longitudinal strip across the mask, particularly at the location of the pleats, it is ensured that the bond between the intermediate layer and the face layer is sufficient for all anticipated uses of the mask, and the potential for adhesive bleed through during the manufacturing process is significantly reduced by minimizing contact with the manufacturing equipment.
The invention will be described below in greater detail with reference to the figures.